It has heretofore been known that quenching of the high temperature pyrolysis gas obtained by the pyrolysis reaction of hydrocarbons is important in order to prevent formed olefins from suffering a loss due to side reactions, but in a practical pyrolysis apparatus, the direct connection of the heating part for pyrolysis to the cooling part of pyrolysis gas is impossible due to a large thermal stress acting in the connecting parts. Accordingly, it has been unavoidable to contrive to install various kinds of thermal-stress-removing parts between the above-mentioned heating part and the cooling part. However, this has not been preferable in the point of olefin yield.
On one hand, in cooling the high temperature pyrolysis gas obtained by the pyrolysis reaction of hydrocarbons, heavier components in the pyrolysis gas at high temperatures form cokes by condensation or polymerization, which block cooling pipes for pyrolysis gas and make the continuous operation of a pyrolysis furnace infeasible. On this account, the removal of cokes has been frequently carried out. However, since it is not permissible for the cooling part for pyrolysis gas to be under thermal stress because of the necessity from its general structure, the cokes cannot be removed by burning. Thus, it has been obliged to stop the feed of raw material hydrocarbons to extinguish the burners of the furnace and stop the operation of the pyrolysis furnace and to carry out the removal of cokes by way of a mechanical process such as washing with a high pressure water, scraping-off with a drill or the like. For the above-mentioned reason, it has been obliged to stop the pyrolysis apparatus for a long period of time.
Under the above-mentioned circumstance, we have been studying in various ways about the quenching apparatus for pyrolysis gas which enables us to attain two objects simultaneously, i.e., a first object of making quenching of pyrolysis gas feasible and a second object of shortening of the term required for decoking.